1,245 research outputs found
Adaptive multi-target tracking in heterogeneous wireless sensor networks
Energy efficient multiple-target tracking
is an important application of Wireless Sensor Networks
(WSNs). Most prior studies consider tracking multiple tar-
gets as an extension of executing a single target tracking
algorithm multiple times, and use a single parameter for
energy efficiency. We consider various factors such as mul-
tiple targets tracked by the sensor, remaining energy of the
sensor and relative location of the sensor with respect to a
target's motion, in order to decide the tracking state of a
sensor in a distributed environment. Further, we explore
and identify the effective combination of these parameters
to optimize energy usage, depending on specific network
conditions. We then propose the Adaptive Multi-Target
Tracking (AMTT) algorithm that can recognize the network
condition based on local information without centralized
coordination, and uses effective parameters to achieve en-
ergy efficiency
Adaptive Random Sampling for Traffic Volume Measurement
Traffic measurement and monitoring are an important component of network management and traffic engineering. With high-speed Internet backbone links, efficient and effective packet sampling techniques for traffic measurement and monitoring are not only desirable, but also increasingly becoming a necessity. Since the utility of sampling depends on the accuracy and economy of measurement, it is important to control sampling error. In this paper, we propose an adaptive packet sampling technique for flow-level traffic measurement with stratification approach. We employ and advance sampling theory in order to ensure the accurate estimation of large flows. With real network traces, we demonstrate that the proposed sampling technique provides unbiased estimation of flow size with controllable error bound, in terms of both packet and byte counts for elephant flows, while avoiding excessive oversampling
NQAR: Network Quality Aware Routing in Error-Prone Wireless Sensor Networks
We propose a network quality aware routing (NQAR) mechanism to provide an enabling method of the delay-sensitive data delivery over error-prone wireless sensor networks. Unlike the existing routing methods that select routes with the shortest arrival latency or the minimum hop count, the proposed scheme adaptively selects the route based on the network qualities including link errors and collisions with minimum additional complexity. It is designed to avoid the paths with potential noise and collision that may cause many non-deterministic backoffs and retransmissions. We propose a generic framework to select a minimum cost route that takes the packet loss rate and collision history into account. NQAR uses a data centric approach to estimate a single-hop delay based on processing time, propagation delay, packet loss rate, number of backoffs, and the retransmission timeout between two neighboring nodes. This enables a source node to choose the shortest expected end-to-end delay path to send a delay-sensitive data. The experiment results show that NQAR reduces the end-to-end transfer delay up to approximately 50% in comparison with the latency-based directed diffusion and the hop count-based directed diffusion under the error-prone network environments. Moreover, NQAR shows better performance than those routing methods in terms of jitter, reachability, and network lifetime
Toward Reliable and Energy Efficient Wireless Sensing for Space and Extreme Environments
Reliability is the critical challenge of wireless sensing in space systems operating in extreme environments. Energy efficiency is another concern for battery powered wireless sensors. Considering the physics of wireless communications, we propose an approach called Software-Defined Wireless Communications (SDC) that dynamically decide a reliable channel(s) avoiding unnecessary redundancy of channels, out of multiple distinct electromagnetic frequency bands such as radio and infrared frequencies.We validate the concept with Android and Raspberry Pi sensors and pseudo extreme experiments. SDC can be utilized in many areas beyond space applications
Network quality aware routing in error-prone wireless sensor networks
We propose a network quality aware routing (NQAR) mechanism to provide an enabling method of the delay-sensitive data
delivery over error-prone wireless sensor networks. Unlike the existing routing methods that select routes with the shortest arrival
latency or the minimum hop count, the proposed scheme adaptively selects the route based on the network qualities including
link errors and collisions with minimum additional complexity. It is designed to avoid the paths with potential noise and collision
that may cause many non-deterministic backoffs and retransmissions.We propose a generic framework to select a minimum cost
route that takes the packet loss rate and collision history into account. NQAR uses a data centric approach to estimate a single-hop
delay based on processing time, propagation delay, packet loss rate, number of backoffs, and the retransmission timeout between
two neighboring nodes. This enables a source node to choose the shortest expected end-to-end delay path to send a delay-sensitive
data. The experiment results show that NQAR reduces the end-to-end transfer delay up to approximately 50% in comparison with
the latency-based directed diffusion and the hop count-based directed diffusion under the error-prone network environments.
Moreover, NQAR shows better performance than those routing methods in terms of jitter, reachability, and network lifetime
Using RTT Variability for Adaptive Cross-Layer Approach to Multimedia Delivery in Heterogeneous Networks
A holistic approach should be made for a wider adoption of a cross-layer approach. A cross-layer design on a wireless network assumed with a certain network condition, for instance, can have a limited usage in heterogeneous environments with diverse access network technologies and time varying network performance. The first step toward a cross-layer approach is an automatic detection of the underlying access network type, so that appropriate schemes can be applied without manual configurations. To address the issue, we investigate the characteristics of round-trip time (RTT) on wireless and wired networks. We conduct extensive experiments from diverse network environments and perform quantitative analyses on RTT variability. We show that RTT variability on a wireless network exhibits greatly larger mean, standard deviation, and min-to-high percentiles at least 10 ms bigger than those of wired networks due to the MAC layer retransmissions. We also find that the impact of packet size on wireless channel is particularly significant. Thus through a simple set of testing, one can accurately classify whether or not there has been a wireless network involved. We then propose effective adaptive cross-layer schemes for multimedia delivery over error-prone links. They include limiting the MAC layer retransmissions, controlling the application layer forward error correction (FEC) level, and selecting an optimal packet size. We conduct an analysis on the interplay of those adaptive parameters given a network condition. It enables us to find optimal cross-layer adaptive parameters when they are used concurrently.IEEE Circuits & Systems Societ
Superconducting transition of a two-dimensional Josephson junction array in weak magnetic fields
The superconducting transition of a two-dimensional (2D) Josephson junction
array exposed to weak magnetic fields has been studied experimentally.
Resistance measurements reveal a superconducting-resistive phase boundary in
serious disagreement with the theoretical and numerical expectations. Critical
scaling analyses of the characteristics indicate contrary to the
expectations that the superconducting-to-resistive transition in weak magnetic
fields is associated with a melting transition of magnetic-field-induced
vortices directly from a pinned-solid phase to a liquid phase. The expected
depinning transition of vortices from a pinned-solid phase to an intermediate
floating-solid phase was not observed. We discuss effects of the
disorder-induced random pinning potential on phase transitions of vortices in a
2D Josephson junction array.Comment: 9 pages, 7 figures (EPS+JPG format), RevTeX
Superconducting phase transitions in frustrated Josephson-junction arrays on a dice lattice
Transport measurements are carried out on dice Josephson-junction arrays with
the frustration index and 1/2 which possess, within the limit of the
model, an accidental degeneracy of the ground states as a consequence of
the formation of zero-energy domain walls. The measurements demonstrate that
both the systems undergo a phase transition to a superconducting vortex-ordered
state at considerably high temperatures. The experimental findings are in
apparent contradiction with the theoretical expectation that frustration
effects in the system are particularly strong enough to suppress a
vortex-ordering transition down to near zero temperature. The data for
are more consistent with theoretical evaluations. The agreement between the
experiments and the Monte Carlo simulations of a model for
suggests that the order-from-disorder mechanism for the removal of an
accidental degeneracy may still be effective in the system. The
transport data also reveal that the dice arrays with zero-energy domain walls
experience a much slower critical relaxation than other frustrated arrays only
with finite-energy walls.Comment: 4 pages, 4 figure
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